(1) Field of the Invention
The present invention relates to the field of capacitors and more particularly to the field of solid state ultracapacitors.
(2) Description of the Related Art
Electrical, electronic, and electromechanical (EEE) parts are used many products. Better energy storage and delivery devices are currently needed. For example, space vehicles use rechargeable batteries that utilize silver zinc or lithium-ion electrochemical processes. These current state-of-the-art rechargeable batteries cannot be rapidly charged, contain harmful chemicals, and wear out early. A solid-state ultracapacitor is an EEE part that offers significant advantages over current electrochemical and electrolytic devices.
Ultracapacitor behavior has been reported in a number of oxides, including reduced barium titanate (BaTiO3 40) and ferroelectric ceramics. BaTiO3 40 is a ceramic material in the perovskite family that possesses a high dielectric constant. Individual coating of ferroelectric BaTiO3 40 grains with a silica (SiO2 48) shell, followed by spark plasma sintering (SPS) in reducing conditions, has been shown to lead to stable ultracapacitor behavior. The permittivity values have been reported to be ≈105 in electroceramics. It has also been shown that treating oxidized BaTiO3 40 at high temperatures in reducing forming gas atmosphere (75-96% nitrogen, N2, and 4-25% hydrogen, H2) produces an N-type semiconducting material. The outer coating, which remains an insulating shell, combines with this semiconducting internal layer, resulting in millions of nanocapacitors in parallel. The combination of a semiconducting grain with an insulating boundary leads to the IBLC effect.
These so-called giant ultracapacitor properties are not easily controlled. American Piezo Ceramics International reports a relative dielectric constant of 1,550 and a dielectric dissipation factor (DF) of 0.5 for single-crystal BaTiO3. High permittivity values such as 10,000 are reported in polycrystalline ferroelectric BaTiO3. Reduced BaTiO3 40 of grain sizes between 70 nm and 300 nm have yielded colossal permittivity values on the order of ≈105 The instant invention was developed by evaluating shell-coated BaTiO3 40 processed under reducing conditions to produce the IBLC effect.